1. Field of the Invention
The present invention relates generally to internal combustion engines in automotive vehicles and, more particularly, to methods of fuel lean-out for an internal combustion engine in an automotive vehicle.
2. Description of the Related Art
Today in automotive vehicles, some automotive vehicle manufacturers use "port-injected" internal combustion engines in their vehicles. In the port-injected engine, a fuel injector sprays fuel into air in an intake manifold of the engine near an intake valve of a cylinder of the engine as the air gets pulled into the cylinder during the cylinder's intake stroke. One problem with fuel delivery to all engines is that some of the fuel remains outside of the cylinder and either remains suspended in charge air or adheres to walls of the intake manifold (i.e., wall wetting). The amount of fuel that ends up adhering to the walls depends on parameters such as manifold temperature, charge temperature, rate of mass airflow, and manifold absolute pressure.
In a deceleration event of the port-injected engine, the manifold absolute pressure and airflow drop, "liberating" fuel from the walls of the intake manifold (i.e., the fuel vaporizes and is transported into the cylinders). Because of this liberation, the amount of fuel delivered by the fuel injectors into the cylinders of the engine must be less than the amount required for stoichiometric balance (i.e., the fuel injection system must be "leaned-out").
Previously, some automotive vehicle manufacturers have used fuel lean-out during deceleration of their port-injected engines. However, these deceleration fuel lean-out features made no distinction between deceleration events of differing severity. As a result, small tip-outs (.i.e., small decreases in throttle openings) could yield relatively poor driveability (due to excessive lean-out) and large tip-outs could yield relatively large hydrocarbon (HC) emissions (due to inadequate lean-out). Further, tip-in transitions from a deceleration event could have inconsistent performance characteristics on the engine depending on what "kind" of deceleration was being exited.
Another problem with all engines is that the throttle position is an inadequate indicator of the airflow into the engine. The throttle position is not linearly related to airflow and, therefore, is difficult to calibrate accurately. A further problem with all engines is that the enrichment required by the engines is different for different speeds and loads.
Additionally, on a "cold start" of the engine (before a catalyst of an exhaust system for the vehicle has had a chance to warm up and become fully active), unburned "long-chained" hydrocarbons (HC) block local oxidation sites on the catalyst, often smothering conversion. This smothering of conversion sites inhibits catalyst "light-off", delaying HC, CO and NO.sub.x conversion. The result is lower conversion efficiencies and higher undesirable emissions over a drive cycle of the vehicle.